The present invention relates to a method and a device for controlling a fuel injection quantity of an internal combustion engine equipped with an auxiliary brake, and more specifically, technology for improving the exhaust property when the auxiliary brake is released.
Brake units used for decelerating and stopping a vehicle can be classified into a main brake for braking a rotary body equipped to wheels and auxiliary brakes other than the main brake. Examples of the auxiliary brake include an exhaust brake for closing a shutter equipped to an exhaust passage to brake the rotary body by means of an exhaust resistance, or an engine brake for discharging compressed air inside a cylinder near the termination of compression stroke to brake the rotary body by means of the throttle loss (Japanese Unexamined Utility Model Publication No. 7-22048).
However, since the operation of the auxiliary brake is accompanied with a time delay, it is likely to cause following problems when releasing the auxiliary brake. That is, when the auxiliary brake is released, a fuel injection quantity is increased from the injection quantity during the operation of auxiliary brake to the injection quantity corresponding to the accelerator opening. Since the increase of fuel injection quantity is performed with good response, fuel tends to be supplied excessively until the release of the auxiliary brake is completed, causing incomplete combustion of the air-fuel mixture to deteriorate the exhaust property.
Therefore, in order to solve the above-mentioned conventional problems the present invention aims at providing a fuel injection quantity control device of an internal combustion engine having improved exhaust property while maintaining good response during release of the auxiliary brake.
In order to achieve the above object, the present invention is constituted such that a judgment is made as to whether an auxiliary brake is operating or not, and when the auxiliary brake is switched from a non-operating state to an operating state, a fuel injection quantity is switched to correspond to an engine operating state while being gradually increased.
More specifically, the constitution of the present invention is such that a basic fuel injection quantity is computed based on the engine operating state, a maximum fuel injection quantity limiting the upper limit of the computed basic fuel injection quantity is computed as a first maximum fuel injection quantity which is the minimum value during the auxiliary brake is operating, and as a second maximum fuel injection quantity that is gradually increased corresponding to the elapsed time from when the auxiliary brake has been released during the auxiliary brake is not operating, and the smaller value between the computed basic fuel injection quantity and the maximum fuel injection quantity is selected as the fuel injection quantity to control a fuel injection device.
According to this constitution, if the auxiliary brake is operating, a first fuel injection quantity is computed as the maximum fuel injection quantity during the operation of auxiliary brake. On the other hand, when the auxiliary brake is not operating, a second fuel injection quantity that is gradually increased corresponding to the elapsed time from when the auxiliary brake is released is computed as the maximum fuel injection quantity. Then, between the computed maximum fuel injection quantity and the basic fuel injection quantity computed based on the engine operating state, the smaller value is selected as a fuel injection quantity, and the fuel injection device is controlled based on the selected fuel injection quantity.
Therefore, if the first fuel injection quantity is set for example to a minimum value (normally xe2x80x9c0xe2x80x9d), the fuel consumption during the operation of auxiliary brake can be restrained. On the other hand, during the auxiliary brake is not operating, since the maximum fuel injection quantity limiting the maximum value of the basic fuel injection quantity is gradually increased corresponding to the elapsed time from when the auxiliary brake has been released, the increase rate is appropriately set so as to enable to avoid excessive fuel supply state that may occur when the auxiliary brake is released. Moreover, the fuel can be injected to the engine even during the acceleration state immediately after release of the auxiliary brake.
In this way, the fuel consumption during the operation of auxiliary brake can be reduced. Further, the exhaust property while maintaining good response can be improved during release of the auxiliary brake.
The constitution may be such that the second fuel injection quantity is increased stepwise corresponding to the elapsed time from when the auxiliary brake has been released.
According to this constitution, when the second fuel injection quantity is computed using a map or a table, memories used for the map and the like can be reduced since the components of the map and the like are reduced.
Further, the constitution may be such that, as the maximum fuel injection quantity, the second fuel injection quantity may be computed by referring to a map in which the fuel injection quantity is set corresponding to the elapsed time from when the auxiliary brake has been released.
According to this constitution, the second fuel injection quantity is computed by referring to the map, to thereby prevent an increase of processing load accompanied by the computation.
Moreover, when a plurality of auxiliary brakes are equipped to the engine, the constitution may be such that, if at least one of the auxiliary brakes is operating, it is judged that the auxiliary brake is operating to compute the maximum fuel injection quantity.
According to this constitution, even when various auxiliary brakes, such as the exhaust brake, the engine brake and the like, are equipped to the engine, the maximum fuel injection quantity during the operation of auxiliary brake is computed if at least one of the auxiliary brakes is operating, thereby capable of reducing the fuel consumption even further.